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Supplementary Materials
BiVO4 Optimized to Nano-Worm Morphology for Enhanced
Kajal Kumar Dey†‖, Soniya Gahlawat†, Pravin P. Ingole†*
† Department of Chemistry, Indian Institute of Technology Delhi,
New Delhi 110016, India.‖Rajendra Singh Institute of Physical
Sciences for Studies and Research, V.B.S. Purvanchal
University, Jaunpur 222003, India
* E-mail: [email protected], Phone: +91 11 2659
7547, Fax: +91 11 2658 1102.
Electronic Supplementary Material (ESI) for Journal of Materials
Chemistry A.This journal is © The Royal Society of Chemistry
2019
mailto:[email protected]
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Figure S1 High resolution TEM micrograph displaying the presence
of several nano-worm BiVO4 particles. Lattice fringes of the
individual particles have been provided below with magnified
cropped portions of the main image.
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Figure S2 FESEM image of the bulk surface morphology of the
BiVO4 particles synthesized followed by 18 hours of hydrothermal
treatment
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50 100 150 200 250 300 350 400 450 5000
20
40
60
80
100
TGA DTA
Temperature/C
Wei
ght %
-2
-1
0
1
2
3
4
5
DTA/V
mg-
1
Figure S3 TGA and DTA curve of BV0 recorded within the
temperature range of 50-500 ⁰C
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Figure S4 (a) TEM micrograph of BV0 showing the coexistence of
sheet-like structures and particles, (b) a magnified portion of BV0
sheet and (c) the corresponding SAED pattern
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Estimation of percentage of nano-worm particles in BVNW
Figure S5 Normalized XRD patterns for BV6 and BVNW
In BV0, tetragonal scheelite particles of BiVO4 are present.
Following the hydrothermal treatment, tetragonal scheelite converts
to monoclinic scheelite BiVO4 with (004) planes being more intense.
Upon 6 hours of hydrothermal treatment we get polycrystalline BiVO4
materials (BV6) with dominant (004) peaks (Figure S5). BV6
contained both BiVO4 sheets along with nanoparticles (Figure 3).
From the normalized XRD pattern of BV6
I(112)/I(004) = 1:0.42 [I(hkl) = intensity of the hkl peak)
The transformation, upon 18 hours of hydrothermal treatment,
eventually leads to the disintegration of BV6 sheets and the
formation of BiVO4 nano-worms having single crystalline (004)
nature (Figure 3). But the overall nature being polycrystalline, as
observed from its XRD pattern (Figure S5), evidently
polycrystalline BiVO4 particles are simultaneously present in this
sample.
From the normalized XRD pattern of BVNW
I(004)/I(112) = 1:0.19
If the fraction of nano-worm particles in BVNW sample is ‘x’;
assuming the nano-worms contribute entirely to I(004) and the other
polycrystalline particles in BVNW contributes to I(004) and I(112)
in the same ratio as in BV6; we have
𝑥 × 1 + (1 ‒ 𝑥) × 1(1 ‒ 𝑥) × 0.42
=1
0.19
or, x = 0.548 or ~55 %
So, roughly, 55% of BiVO4 particles in BVNW are the
nano-worms.
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It should be mentioned that this estimation method is not
entirely accurate as some of the approximations are pretty loose,
e.g. ‘other polycrystalline particles in BVNW contributes to I(004)
and I(112) in the same ratio as in BV6’, may not hold up entirely,
as the morphology evolution and concomitant crystallographic
transformation are dynamic process; so, that ratio will probably
not be same. However, we can get a decent enough approximation
using this method.
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Figure S6 (a) HRTEM micrograph of BV6. The rectangular boxes
represent the crystallographic defect areas; (b), (c) and (d)
provides magnified version of those defects. The solid lines
indicate the grain boundaries.
Figure S6 reveals crystallographic defect structures associated
with BV6 nanoparticles observed
through the TEM micrographs. It is well known that the presence
of crystallographic lattice defects
such as grain boundary can impede charge carrier transfer as
such defects tend to act as potential
barriers. These kinds of defects can be particularly pronounced
during incomplete growth of
particles undergoing constant changes in the form of
dissolution, nucleation and growth. BV6
represents an initial phase during the hydrothermal treatment of
Scheelite tetragonal BiVO4 sheets
evolving into the nano-worm like particles. Grain boundary
usually is a feature of polycrystalline
materials and indicates the interface between two crystallite
regions where the (hkl) planes of both
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terminate suddenly. In figure S6(a) we have selected three such
regions enclosed by rectangular
boxes that contain the grain boundary (GB) between different
crystallite regions. Subsequent three
figures i.e. S6 (b), (c) and (d), represents magnified versions
of these defects where the GBs have
been identified by solid lines. S6(b) represents the GB between
(004) and (024) crystallite regions.
S6(c) represents the GB between (002) and (004) crystallite
regions and S6(d) represent the GB
between (020) and (112) crystallite regions. There are numerous
such regions but we chose to
highlight three of them for the sake of simplicity. Presence of
such a defect rich structure is a direct
consequence of BV6 being an intermediate during the morphology
transformation. It also
underscores the presence of numerous potential barriers in the
BV6 structure that inhibits the
charge transfer and limiting the photoelectrochemical
performance of this material.
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Figure S7 Plots of space charge layer width against the applied
potential for the BiVO4 samples
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Figure S8 (a) and (b) CVs recorded for BVNW and BV12 at various
scan rates in the phosphate buffer solution (pH 7.00). (c) linear
fitting of Δ (current density) vs scan rates at 0.05 V vs
Ag/AgCl.
Electrochemically active surface area (ECSA) of the samples were
estimated via double layer capacitance method 1using cyclic
voltammetry (CVs) recorded in the non-Faradaic region (-0.5 V to
0.6 V vs Ag/AgCl). CVs were recorded at different scan rates e.g.
10, 20, 30, 40, 50, 75, 80 and 100 mV/s (Figure S7 (a) and (b)).
The difference in current density (Δ (current density)) between the
anodic and cathodic current at the potential of 0.05 V was
calculated from the CV curves recorded at each of the scan rates. Δ
(current density) was plotted against corresponding scan rates for
both BV12 and BVNW (Figure S7 (c)) and half of the slope of the
linear fitted plots is taken as the double layer capacitance (Cdl).
The ECSA values are usually accepted as proportional to the
corresponding Cdl values. Here, the obtained Cdl values for BV12
and BVNW electrodes are 253.42 F cm-2 and 269.54 F cm-2.
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Calculation of Charge transport efficiency (ηtrans)
Chopped LSV measurement was carried out in Phosphate buffer
solution (PBS; pH 7.00). The
corresponding photocurrent is expressed as . 𝐽𝐻2𝑂
PEC measurement with hole scavenger was recorded in PBS solution
with the addition of 0.5 (M) sodium sulfite. The pH was adjusted to
7.00 and the corresponding photocurrent is expressed as
. 𝐽𝑁𝑎2𝑆𝑂3
Charge transport efficiency (ηtrans) is calculated as 𝜂𝑡𝑟𝑎𝑛𝑠
=
𝐽𝐻2𝑂𝐽𝑁𝑎2𝑆𝑂3
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Figure S9. Light harvesting efficiency of the photoanodes
Light harvesting efficiency (LHE) of the photoanodes was
calculated by following the equation:
𝐿𝐻𝐸 = 1 ‒ 10 ‒ 𝐴(𝜆)
Where, A = absorbance at wavelength λ.
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Figure S10. Chopped J-V curves for BVNW and BV12 recorded in
phosphate buffer solution in presence of 0.5 (M) Na2SO3.
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Figure S11. Left side-high resolution TEM micrograph of a fully
grown BiVO4 nanoworm (BVNW). Right side- significant portion of a
relatively wide BV12 rod. Individual particles are bound by dashed
yellow lines.
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Q (CPE) Parameters
Sample
RS/Ω (RCT/Ω)/105
(Y0/F)/10-5 n
BV0 14.13 2.959 2.569 0.96
BV6 16.39 3.933 2.78 0.95
BV12 13.78 2.289 2.736 0.94
BVNW 15.08 1.091 3.294 0.95
Supplementary References
1 K. K. Dey, S. Jha, A. Kumar, G. Gupta, A. K. Srivastava and P.
P. Ingole, Electrochim. Acta, 2019, 312, 89–99.
Table S1 Tabular representations of the electrical components
obtained from fitting the experimental EIS data in an appropriate
circuit model
